I can’t find any relevant literature / nobody has studied my topic
Usually the reason is that your search is not broad enough. The fix is simple: zoom out.
Go back to your Introduction and ask yourself:
- What were my study aims?
- What was I trying to find out?
- Why am I trying to do this research? What was the bigger reason?
Then start looking at what other people have done in that area.
For example, say you’re studying the breaking strength of branches of three tree species, and a search for those species finds nothing. The bigger reason was to decide which trees to plant in a windy city. So zoom out: search for wind damage to urban trees, tree failure in storms, or the mechanical properties of branches in other species.
Finding literature means zooming out
The Discussion requires that you generalise your results, so literature on the broader topic is what you’ll need to compare with anyway. For more on how to do this, see Discussion repeats Results